A method for previously setting up a tube for air pressure installation at an optical fiber installation spot and then installing an optical fiber unit in the tube by air pressure is very widely used as an optical fiber installation technique at a narrow space such as FTTH (Fiber To The Home) since it ensures easy installation and removal of the optical fiber unit and requires low costs for construction.
FIG. 1 is a perspective view showing an appearance of a general optical fiber unit for air pressure installation, commonly called as ABF (Air Blown Fiber).
Referring to FIG. 1, the optical fiber unit U includes an optical fiber bundle 10 commonly having 1 to 12 cores, and a buffer coating layer 11 formed on the bundle 10. On the surface of the buffer coating layer 11, glass beads 12 are additionally formed to decrease fractional force with the inner surface of the tube for air pressure installation and increase drag force caused by the air pressure. When required, a polymer foaming layer or a Teflon coating layer may be provided on the buffer coating layer 11 in order to increase the drag force.
FIG. 2 is a schematic view showing a conventional air pressure installation apparatus which inserts the optical fiber unit U configured as above into a tube by means of air pressure.
Referring to FIG. 2, the conventional optical fiber unit installation apparatus includes an optical fiber unit supplier 20, a blowing head 21 having an entrance A into which the optical fiber unit U successively provided from the optical fiber unit supplier 20 is introduced and an exit B communicated with the entrance A and combined with an air pressure installation tube 22, a pressing unit 26 for applying a compressed air to the exit B of the blowing head 21 so that the optical fiber unit U introduced into the entrance A is inserted into the air pressure installation tube 22, a driving roller unit 23 for pushing the optical fiber unit U into the air pressure installation tube 22 with rotating on both sides of the optical fiber unit U, and a buckling sensor 25 for sensing that movement of the optical fiber unit U is prohibited in the tube 22 by an obstacle and then stopping the installation.
In the conventional optical fiber unit installation apparatus, the optical fiber unit U, continuously introduced into the blowing head 21, is inserted and installed in the installation tube 22 by the air pressure provided from the pressing unit 26 with controlling its advancing speed by the driving roller unit 23.
Meanwhile, the blowing head 21 has a sealing unit 24 to prevent the compressed air supplied from the pressing unit 26 from flowing backward toward the entrance of the optical fiber unit U. Conventionally, the sealing unit 24 having a shape of such as O-ring is adhered to the outer circumference of the optical fiber unit U in order to effectively prevent backward flow of the fluid.
However, the surface of the optical fiber unit U has very weak structure since the glass beads 12 are formed thereon. Thus, if the sealing unit 24 is installed in contact with the outer circumference of the optical fiber unit U, the surface may be damaged while the optical fiber unit U passes through the sealing unit 24 during installation.
In such a reason, the sealing unit 24 is not contacted with the outer circumference of the optical fiber unit U but has a predetermined gap. Accordingly, while the air pressure installation is conducted using the conventional optical fiber unit installation apparatus, a significant amount of fluid is flowed backward toward the entrance A and leaked through the gap between the sealing unit 24 and the outer circumference of the optical fiber unit U, thereby causing noise and deteriorating installation performance and efficiency of the pressing unit 26.